In this study, the interfacial reactions and mechanical properties of solder joints after multiple reflows were observed to evaluate the applicability of the developed materials for high-temperature soldering for automotive electronic components. The microstructural changes and mechanical properties of Sn-Cu solders regarding Al(Si) addition and the number of reflows were investigated to determine their reliability under high heat and strong vibrations. Using differential scanning calorimetry, the melting points were measured to be approximately 227, 230, and 231 °C for the SC07 solder, SC-0.01Al(Si), and SC-0.03Al(Si), respectively. The cross-sectional analysis results showed that the total intermetallic compounds (IMCs) of the SC-0.03Al(Si) solder grew the least after the as-reflow, as well as after 10 reflows. Electron probe microanalysis and transmission electron microscopy revealed that the Al-Cu and Cu-Al-Sn IMCs were present inside the solders, and their amounts increased with increasing Al(Si) content. In addition, the Cu6Sn5 IMCs inside the solder became more finely distributed with increasing Al(Si) content. The Sn-0.5Cu-0.03Al(Si) solder exhibited the highest shear strength at the beginning and after 10 reflows, and ductile fracturing was observed in all three solders. This study will facilitate the future application of lead-free solders, such as an Sn-Cu-Al(Si) solder, in automotive electrical components.

Today, many workers are exposed to physical and mental stress due to various poor working conditions in modern society, so, the mental health of workers is in a serious condition and workers’ stress is associated with depression and suicide. Hence, it is important to prevent mental stress and alleviate mental illness. The purpose of this study is to examine the mediating effect of depression and the control of social support or the controlled mediating effect of social support on the suicidal ideation of social welfare facility workers who are expected to have more stress than workers in other jobs. The subjects of the study are randomly sampled 323 workers from the workplaces located in one province, and the data is analyzed using correlation analysis, IBM SPSS 27.0 Kor and SPSS Process Macro process type 4. Type 1. Type 14, bootstrapping is used for mediating effect verification. The results of the study are as follows. First, there was a significant correlation between workers' job stress, depression, social support, and suicidal ideation. Second, workers' job stress was found to be an important factor in increasing suicidal ideation through depression as meditation. Third, by controlling social support the depression of workers was found to be a factor that alleviated suicidal ideation. Fourth, the social support had a controlled mediating effect because the influence of job stress on suicidial ideation by depression depends on the level of social support. In this study, the buffer effect of social support is confirmed, but in the previous studies on social support did not show consistent results of buffer effect. The findings suggest the importance of social support as a buffer effect of job stress and depression. So, it is hoped that more research should be carried out on the role of social support in the future because the role of social support, the external environment surrounding workers, helps prevent and alleviate problems of mental health of workers in social welfare facilities or other jobs.